The assembler directive used to give name to some value or symbol for 8086 ASM-86 is
EQU
EQU — short for "equate" — is the directive that binds a name to a value, option 3.
PORT_A EQU 80HCOUNT EQU 100
Thereafter the assembler substitutes the value wherever the name appears, so MOV AL, COUNT assembles exactly as MOV AL, 100 would.
| Directive | Purpose |
|---|---|
| DD | Define Doubleword — reserves and initialises 4 bytes of storage |
| NAME | Gives a name to the assembly module, for the linker |
| EQU | Equates a symbol to a value or expression |
| PROC | Marks the start of a procedure, with NEAR or FAR |
The distinction that matters — EQU against DD. This is the real point of the question. A data-definition directive such as DB, DW or DD allocates memory: the value is placed in the object file and occupies an address at run time, and it can be read or written. EQU allocates nothing. It is a purely assembly-time substitution, resolved before any code is generated, so the value has no address and cannot be modified. Using EQU for a constant therefore costs no memory and no fetch cycle.
Why option 2 is tempting. "NAME" sounds like exactly what "give name to some value" describes, but NAME names the module, not a value — a piece of bookkeeping for the linker when several object files are combined. There is no value involved at all.
What EQU is used for in practice. Port addresses, buffer sizes, bit masks, delay counts — anything that appears repeatedly and might need changing. Defining MAX_LEN EQU 64 once and referring to the name everywhere means a single edit changes the program consistently; scattering the literal 64 through the source invites the classic bug of changing some occurrences and not others. It is also self-documenting: CMP AL, MAX_LEN says what it means in a way CMP AL, 64 does not.
A related directive is = in MASM, which also equates a symbol to a value but, unlike EQU, permits the symbol to be redefined later in the file.
Hence, the directive is EQU.
Similar Questions
A microprocessor is a semiconductor chip fabricated with entire central processing unit (CPU) on it. It is a programmable device that accepts binary data from an input device, processes the data according to the instructions stored in the memory and provides results as output. Basically microprocessor performs two functions - (a) Fetches an instruction from the memory and (b) Performs the operation specified by the instruction. There are special inputs to the microprocessor called interrupts. External devices use these interrupts to get the microprocessor attention. A micro computer can be built by using 8085 microprocessor along with many other chips such as 8155, 8255, 8279, 8253, 8257, 8259, 8251 etc. 8085 microprocessor is 8-bit microprocessor which has 8-bit data registers where as 8086 is a 16-bit microprocessor.
The following 8051 assembly program is given. Answer the questions based on it.
Line No. Mnemonics 1 MOV SP, #4F H 2 SET B PSW.3 3 MOV R0, #25H 4 MOV R1, #0AH 5 MOV R2, #06H 6 PUSH 8 7 PUSH 9 8 PUSH 0AH . . . V V 20 POP 8 $D_7$ $D_6$ $D_5$ $D_4$ $D_3$ $D_2$ $D_1$ $D_0$ In 8255 programmable peripheral interface device, if the port A and port B are to be set in a hand shake mode along with port C, what are the bits in the 8 bit control word to be set as 0 1 0.
The number system for the machine code of the microprocessor 8085 is
Which of the options in a multipurpose instruction used to implement the interrupt of 8085 and serial data input ?
Both 8155 and 8255 programmable peripheral interface ICs have the following common features :
(i) Programmable I/Os
(ii) Either port A or Port B can be set as either input or output ports.
(iii) One 14-bit down counter
(iv) AD0 – AD7 are multiplexed address/datalines.Each instruction in an assembly program has the following fields :
(i) Lable field
(ii) Operand field
(iii) Comment field
(iv) Mnemonic fieldPlease write the proper sequence of fields :
The mnemonic of 8085 processor indicate :
List – I List – II a. RLC i. Rotate Accumulator Right through carry b. RRC ii. Rotate Accumulator Left through carry c. RAR iii. Rotate Accumulator Left d. RAL iv. Rotate Accumulator Right Codes :
Match the following :
List – I (Pin terminals) List – II (Applications) a. SID, SOD i. Wait state b. READY ii. Serial data transfer c. TRAP iii. Address Latch Control d. ALE iv. Interrupt Codes :
Assertion (A) : In serial communication system, when the transmission of data goes in both ways, it is called full-duplex system. Now if two micro processors are connected in full duplex mode, the amount of data transmitted will be double to the amount of data in half-duplex mode connection.
Reason (R) : When the transmission of data goes in one way, it is called half-duplex system and when the data moves in both ways, it is called full duplex system.
Important Questions from Microprocessors
An 8086 address bus is a/an _____ -bit bus
Program counter for any counter:
In the pin out configuration of the 8085 microprocessor, the sequential input data is represented by
Which of the following functions is not performed by a microprocessor?
Match the columns.
Pin
Description
a. D 0-D 7
1. Reset Input
b. RESET
2. Data Lines
c. A 0,A 1
3. Internal Address
